In these days, electrophotographic copying machines such as a full-color copying machine are in practical use. When transferring a toner image which is developed on a photoreceptor on to a sheet of paper, a process is employed of transferring the toner image on to the sheet of paper after the toner image is copied on a transfer intermediate body.
One example of the above is shown in FIG. 3. Namely, in this process, after the surface of a photosensitive drum 1 is charged by a charging roll 2, a slit exposure 4 of a light image of a subject copy reaches the surface of the photosensitive drum 1 through an exposure mechanism member 3. Thereafter, an electrostatic latent image which corresponds to the image of the subject copy is formed on the surface of the photosensitive drum 1, and a toner image is formed by supplying a developing agent by a developing apparatus 5. An endless belt 6, a transfer intermediate body, is contacted with pressure by a primary transfer roller 7 to the lower side of the photosensitive drum 1. The toner image developed on the photosensitive drum 1 is transferred, in a primary transfer, on to the surface of the endless belt 6 in the order of colors by repetitive forward and backward movements of the endless belt 6. Then, in a secondary transfer, the toner image is transferred on to a sheet of paper 9 which is put between the endless belt 6 and a secondary transfer roller 8 by the forward movements (which is the same direction of the photosensitive drum 1) of the endless belt 6. In the meantime, the developing agent remaining on the surface of the endless belt 6 after the secondary transfer is withdrawn by a cleaning blade 10, whereby the endless belt 6 is supposed to be ready for the next transfer. The developing agent remaining on the surface of the photosensitive drum 1 after the primary transfer is withdrawn by a cleaning apparatus 11, and the electricity of the surface of the photosensitive drum 1 then is removed by an eraser lamp 12.
Conventionally, the endless belt 6 has been formed from a conductive material in which polycarbonate (hereinafter, referred to as "PC") and a conductive agent such as carbon black, graphite and/or the like are melted and kneaded, and the volume resistivity thereof is adjusted. However, since the PC is inferior in flex fatigue resistance, cracks occur after long time use, resulting in the problem of poor durability. Moreover, since the PC is high in polarity, releasability of the toner image from the endless belt 6 (hereinafter, referred to as "toner releasability") becomes poor, and the developing agent sticks on the belt's surface with time, whereby causing a problem of a bad effect to images.